Loudspeaker magnet structure



Oct. 22, 1968 1. W. GOSMA LOUDSPEAKER MAGNET STRUCTURE Original Filed June 4. 1965 A TTORNEY United States Patent C) 3,407,371 LOUDSPEAKER MAGNET STRUCTURE John W, Gosma, Kokomo, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Original application June 4, 1965, Ser. No. 461,285, now Patent No. 3,354,541, dated Nov. 28, 1967. Divided and this application Sept. 26, 1967, Ser. No. 670,556

3 Claims. (Cl. 335-231) ABSTRACT F THE DISCLSURE A loudspeaker magnet assembly which includes a metallic casing, having an inner lining of insulating resilient material, crimped over a permanent magnet and subassembly leaving one face of the resultant assembly open so that a desired driving means may be interposed adjacent the core of the assembly.

This application is a division of my copending United States patent application Ser. No. 461,285 Gosma, entitled Loudspeaker Magnet Structure and Method of Assembling Same, which was led on lune 4, 1965, and which is now United States Patent No. 3,354,541.

This invention relates to a loudspeaker magnet structure.

The majority of current loudspeaker assemblies utilize permanent magnet structures to provide the field in which the voice coil is suspended and in which it moves to drive the diaphragm connected thereto to create and reproduce sound. Since stereo and multiple speaker outlets from a given receiver are now more common loudspeaker production is high and cost is an important factor. One further impetus to speaker production is due to the introduction on the market of stereo systems for automotive use that require four speakers.

It is an object in making this invention to provide a unitary magnet and casing assembly that is low in cost and simple to assemble with the frame for the speaker.

With this and other objects in view which will become apparent as the Specification proceeds, my invention will be best understood by reference to the following specification and claims and the illustrations in the accompanying drawings, in which:

FIGURE 1 is a side elevational view of a loudspeaker assembly embodying the invention, parts being broken away and shown in section; and

FIG. 2 is an exploded view showing the parts of the magnet assembly in spaced relation.

The basic drive unit in this instance is formed of a ceramic magnet 2 having a top pole plate 4 and a bottom pole plate 6. These magnets may be made of hard ferrites and are rather brittle requiring care in applying the housing or they might be cracked. The magnet 2 is of annular form having a central opening 8 therein. It is proposed to encase this basic assembly of the magnet with its top and bottom pole plates in a casing or housing of aluminum and then applying a strong magnetic iield to cause the casing to wrap tightly around the subassembly to form a complete unitary member. Such a casing 10 is shown in the form of a cup having cylindrical side walls and a bottom surface but an open top. If it were attempted to assemble the magnet within the casing by folding over the upper edge either mechanically or by applying a strong magnetic lield through the use of such a device as a Magneformer the ceramic magnet might be cracked. It is, therefore, necessary to apply some lining shock absorbent material to protect the same.

It has been found that a polyvinylchloride material works well in this instance and a layer of such material 12 is shown in the bottom of the cup or casing 10 in ICC FIG. 2. The amount of polyvinylchloride material used should be suicient to surround the magnet on the sides and extend a short distance out over the top edge in the final assembly. The casing 10 is, therefore, first filled to the desired point with the polyvinylchloride material or some similar material which is electrically insulating and will provide shock proofing. The lower plate 6, the magnet 2 and the upper plate 4 are then placed in the casing in sequence and properly located one upon the other. By slight pressure from the top of the polyvinylchloride material will be forced up around the edges of the magnet parts and out over the top corner for a short distance to insulate and mount the magnet and poles. This subassembly is then placed in an oven at an elevated temperature and cured at, for example 375, the temperature being determined by the material being used. This sets the polyvinylchloride so that it becomes rubbery and holds the magnet assembly in place.

This assembly is now placed in a Magneformer which is a well known commercial device capable of applying a strong magnetic field to deform material through discharge of a condenser. Upon actuation of the device the top edge of the casing 10 is folded in tightly over the magnet, as shown at 26 in FIG. l, in a quick and single action to make a permanent magnet unit for a loudspeaker.

As shown on the drawing, the lower plate 6 has a central opening 14 which may be internally threaded and into which may be screwed a short stud 16 integral with a central core member 18. This is inserted into the central aperture to form a gap with the upper plate and an aperture into which the voice coil 20 of the speaker may project and in which it is supported. The top plate 4 of the speaker is also provided with a series of regularly spaced rivets 22 which when brought into juxtaposition with the frame 24 of the speaker are adapted to project into mating openings therein and then peened over to secure the magnet unit to the speaker frame. These could, of course, be drilled out and threaded and screws could be used for securing the unit as Well as the riveted members.

It will be obvious that this is a very simple, fast and inexpensive manner in which to quickly form magnet assemblies for loudspeakers and to assemble the same to loudspeaker frames.

What is claimed is:

1. A magnet structure comprising a metallic casing lined with a thin layer of insulating, resilient material, a permanent magnet and pole assembly supported in the layer of material, said casing closely conforming to the coniiguration of said permanent magnet and pole assembly but being spaced therefrom by means of said layer of insulating, resilient material, one face of said casing being crimped over to lock the permanent magnet and pole assembly in place, said face being open so that desired driving means may be interposed adjacent the core.

2. The device as claimed in claim 1 in which the permanent magnet is of the ceramic type.

3. The device as claimed in claim 1 in which the permanent magnet is of the ceramic type and the insulating, resilient material is polyvinylchloride.

References Cited UNITED STATES PATENTS 3,191,421 6/ 1965 Coen.

FOREIGN PATENTS `872,194 7/ 1961 Great Britain. 935,948- 9/ 1963 Great Britain.

GEORGE HARRIS, Primary Examiner. 

